Abstract O-GlcNAcylation is an intracellular posttranslational glycosylation that is greatly enhanced under hyperglycemic conditions such as diabetes. We found that hyperglycemia induces O-GlcNAcylation of the transcription factor nuclear factor kappa B (NF-?B) subunit c-Rel at serine 350. c-Rel is predominantly expressed in T and B cells and controls cell proliferation, survival, and host defense. We discovered that O- GlcNAcylation of c-Rel in T cells regulates the induction of a subset of genes that may exacerbate T cell-mediated autoimmunity. Autoimmune diabetes is also associated with deregulated B cell function and autoantibody production. Both c-Rel and global O- GlcNAcylation, have been shown independently, to be essential for the regulation of B cell function. However, the specific role of c-Rel O-GlcNAcylation in B cells remains unknown. We hypothesize that c-Rel O-GlcNAcylation is a critical regulator of B cell survival and function as well as altered antibody class switching and autoantibody production in type 1 diabetes. Here we propose to study the role of c-Rel O- GlcNAcylation in B cells by reconstitution of non-O-GlcNAcylatable mutant c-Rel in our novel c-Rel deficient non-obese diabetic mouse model and cellular systems. This study will (a) ascertain c-Rel O-GlcNAcylation as a novel mechanism regulating transcription and autoantibody production in B cells and (b) reveal a long-sought-after specific molecular drug target for the development of new therapeutics to control autoimmunity in diabetes. This foundational study will also have broad future translational implications in O-GlcNAcylation-dependent dysregulation of B cell functions in type 1 and type 2 diabetes as well as obesity, where hyperglycemia is involved as a common factor.